The invention relates to a weaving machine, and to an apparatus and method for tucking in one or more weft thread ends and for forming a cloth edge.
In order to form a firm cloth edge, the weft threads which are inserted into a shed in a weaving machine are severed at their ends with excess length after completion of the weft insertion and the free ends are bent into the open shed after the next change of shed but before the next beating up of the weft thread. As a rule the procedure for the bending in, which is designated as tucking in of the weft thread in technical textile terminology, takes place either mechanically, pneumatically or pneumo-mechanically. An example of a mechanical selvedge tucking apparatus with a strip tucking needle is disclosed for example in the published document DE-AS 1 710 353. An example of a pneumo-mechanical embodiment is known from EP-A-0 134 377. In this pneumo-mechanical embodiment a tucking needle with an eye is used into which the thread end is threaded by means of compressed air. The disadvantage of both the mechanical and the pneumo-mechanical selvedge tucking apparatuses consists in that their use is restricted to certain maximum speeds of rotation of the weaving machine, which is caused by the mechanical processes.
In order nevertheless to enable higher speeds of rotation of the weaving machine in the manufacture of cloths with selvedges, purely pneumatic selvedge tucking apparatuses, so-called air tuckers, are used. A typical example of a pneumatic selvedge tucking apparatus of this kind, which is also designated as an air strip tucker or air tucker, can be found in the specification EP-A-1 088 922. The selvedge tucking apparatus which is described in this document includes a nozzle arrangement with a plurality of nozzles which is arranged outside the cloth width in order to blow the weft thread ends into a shed.
In the case of soft and pliable weft yarns the known tuckers from the prior art normally function in a problem-free manner. However, as soon as harder and/or stiffer yarns are used, it becomes increasingly more difficult to produce an unobjectionable cloth edge. Thus e.g. the thread ends of stiffer yarns can completely or partially jump back from the tucked in position and/or the thread ends of yarns of this kind can completely or partially penetrate through the upper or lower shed before the thread ends together with the following weft threads are beaten up and bound in. The penetration of the weft thread ends through the upper or lower shed is also designated as bleeding through. As a result of the weaving errors which are caused by the improper tucking in of the weft thread ends the cloth is classed as inferior. Problems can also arise with normally pliable yarns when a plurality of weft thread ends, e.g. two, are tucked into the same shed. In this case, frequently one weft thread end is properly tucked in whereas the other weft thread end is improperly positioned and e.g. can bleed through.